Liquid-metal-filled rotor blade

ABSTRACT

A hollow turbine blade is filled with a liquid metal which is cooled by means of a plurality of tubes through which coolant air is passed. The walls of the turbine blade are in contact with the liquid metal which acts as the heat exchange mechanism, the air acting as the system coolant.

' United States Patent 2.879.028 3/l959 Stalker 4 1 6/90 3.045.965 7/1962 Bowmer 416/90 3164.367 l/l965 Lynch i 4 l 6/96 X 3,314,650 4/[967 McCormick 416/96 3.402.9l4 9/l968 Kump et al. 4l6/97 X FOREIGN PATENTS 760.734 1 1/1956 Great Britain 4 1 6/97 Primary Examiner- Everette A. Powell, Jr. Attorneys-Charles M. Hogan and lrwin P. Garfinkel ABSTRACT: A hollow turbine blade is filled with a liquid metal which is cooled by means ofa plurality of tubes through which coolant air is passed. The walls of the turbine blade are in contact with the liquid metal which acts as the heat exchange mechanism. the air acting as the system coolant.

1 LIQUID-METAL-FILLED ROTOR BLADE BACKGROUND OF THE INVENTION There is at the present time a demand for the reduction in size of gas turbine engines while at the same time increasing output power. As a result turbine operating temperatures greatly exceed the temperatures which modern superalloy materials can withstand. Because of this it has been necessary to cool the components of the modern high-performance engines, one of the most critical components being the first stage turbine rotor blade.

There are many prior art arrangements for cooling turbine blades. The most common is the air-cooled hollow blade. An example of this is Banthin U.S. Pat. No. 3,370,829 assigned to the same assignee as this invention. The prior art also teaches the use of water-cooled turbine blades, for example, Eckert, U.S. Pat. No. 2,788,601. Furthermore, the prior art has made use of hollow blades filled with liquid'metals; for example, Constant, U.S. Pat. No. 2,565,594.

The present invention is an improvement over the prior art in that it makes use of a liquid metal which serves as the system heat exchanger and a coolant fluid which removes the heat from the liquid.

SUMMARY OF THE INVENTION It is well known that a turbine blade can be cooled by using many small-diameter holes through which coolant air is passed. Such an arrangement produces a low convective resistance for the coolant air, and thus a high cooling effectiveness can be achieved. The effectiveness of this method would be improved even further if the conductive resistance of the blade material could be reduced. By using a liquid metal in lieu of the solid metal, the conductive resistance is decreased considerably for two reasons. First of all the conductivity of a liquid metal may be as much as four times that of modern blade materials and, second, the heat transfer coefiicient, due to natural convection in a high centrifugal field, is very high. Therefore, liquid metal such as sodium or a sodium-potassium alloy offers negligible resistance to the flow of heat and it tends to keep the metal temperature more uniform, thus reducing thermal stresses.

The present invention provides a hollow rotor blade which uses a liquid metal as a heat exchange mechanism and which uses air as the coolant. The air enters the blade at the root and passes through small tubes to a collection region at the blade tip. Small tubes pass through the liquid metal which is in an entirely filled, hermetically sealed chamber. The air absorbs the heat which is transported from the outside blade walls via the liquid metal. The liquid metal heats up at the outside walls and is forced radially inward due to its lower density and the high centrifugal field of the rotating blade. The liquid metal at the tube walls becomes more dense and is forced radially outward. Thus, the centrifugal field, in combination with the density change, sets up a free convection process for the liquid metal. As the air leaves the tubes it cools the tip region by impingement. The air then flows radially inward and escapes to the outside.

THE DRAWINGS FIG. 1 is a side elevation partly in section of a turbine blade made in accordance with this invention;

FIG. 2 is a cross section taken through the line 2-2 in FIG. I; and

FIG. 3 is a cross section taken through the line 3-3 in FIG. 2.

DESCRIPTION OF THE INVENTION The rotor blade generally indicated at consists of a hollow metal airfoil-shaped portion 12 which is located in the hot gas stream of a turbine, and a root 14 adapted to be connected to a rotating turbine wheel (not shown). The airfoil-shaped portion 12 of the blade 10 is divided by a wall 11 to provide two internal chambers, a liquid metal chamber 16 and an air chamber 18. The liquid metal chamber 16 is radially traversed by a plurality of hollow tubes 20 extending through an inner wall 21 and the wall 11, thus providing a coolant passage from a coolant entry 22 at the root 14 to the coolant chamber 18. The tubes 20 are sealed in the walls 11 and 21 so that when filled with a liquid metal 24, the liquid metal is hermetically sealed within the chamber 16.

Coolant air leaving the tubes 20 cools the tip 26 of the turbine blade and then leaves the chamber 18 through a slot 28. The air then exists from the blade through a porous trailing edge transpiration panel 30.

In use the turbine blade is mounted on a rotating turbine wheel, and hence is subject to a large centrifugal field. When the liquid metal heats up at the outside walls, it becomes less dense than the liquid metal at the tubes 20 which is cooled and becomes more dense. The heated less dense metal is forced radially inward because of the high centrifugal field, while the higher density metal is forced radially outward. Thus, the combination of the centrifugal field along with the density change due to temperature sets up a free convection process for the liquid metal.

As the coolant leaves the tubes 20 it cools the tip region 26 by impingement. The coolant then flows radially inward and escapes to the outside through the slot 28 and the transpiration panel 30.

In practice the liquid metal is preferably sodium or a sodium-potassium alloy, but other metals having the proper characteristics may also be used. The coolant fluid contemplated for use by this invention is air, but any available relatively cool fluid may be used. Furthermore, while the disclosed turbine blade utilizes a transpiration panel 30, the coolant air may simply be discharged from an appropriately shaped slot.

Iclaim:

l. A hollow turbine blade, a sealed chamber in said blade, said chamber being filled with a liquid having a relatively high heat conductivity as compared with said blade, a plurality of hollow coolant tubes extending through said chamber, said tubes providing a coolant passage from outside said blade and through said chamber, said coolant tubes being in direct contact with said liquid, a collecting chamber in said blade, said tubes exhausting into said collecting chamber, and outlet means in said chamber for exhausting said coolant from said blade.

2. The invention as defined in claim I wherein said liquid is a metal.

3. The invention as defined in claim 2 wherein said metal is selected from a group consisting of sodium and sodium-potassium alloys.

4. The invention as defined in claim 1 wherein said outlet means includes a transpiration panel.

5. A cooled turbine blade comprising:

a root portion connectable to a rotating wheel and a hollow airfoil-shaped portion radially extending from said root portion;

a sealed chamber and a collecting chamber in said airfoilshaped portion, said sealed chamber extending radially from said root along the leading edge of said airfoilshaped portion; 2

a plurality of hollow coolant tubes extending through said sealed chamber and providing coolant passages from the exterior of said blade to said collecting chamber;

a liquid metal filling said sealed chamber; and

outlet means for exhausting coolant from said collecting chamber.

6. The invention as defined in claim 5 wherein said liquid is a metal.

7. The invention as defined in claim 6 wherein said metal is selected from a group consisting of sodium and sodium-potassium alloys. I

8. The invention as defined in claim 5 wherein said outlet means includes a transpiration panel.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,623,825 Dated November 30 1971 William F. Schneider Inventor(s) It: is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown beluw:

Column 1, line 18 "Patent No. 2,788,601" should "exists" should read exits Signed and sealed this 31st day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents RM PO-105O (10-69] uscoMM-oc B0376-F'69 9 U5. GOVERNMENT PRINTING OFFICE Nil 0-356-43L 

1. A hollow turbine blade, a sealed chamber in said blade, said chamber being filled with a liquid having a relatively high heat conductivity as compared with said blade, a plurality of hollow coolant tubes extending through said chamber, said tubes providing a coolant passage from outside said blade and through said chamber, said coolant tubes being in direct contact with said liquid, a collecting chamber in said blade, said tubes exhausting into said collecting chamber, and outlet means in said chamber for exhausting said coolant from said blade.
 2. The invention as defined in claim 1 wherein said liquid is a metal.
 3. The invention as defined in claim 2 wherein said metal is selected from a group consisting of sodium and sodium-potassium alloys.
 4. The invention as defined in claim 1 wherein said outlet means includes a transpiration panel.
 5. A cooled turbine blade comprising: a root portion connectable to a rotating wheel and a hollow airfoil-shaped portion radially extending from said root portion; a sealed chamber and a collecting chamber in said airfoil-shaped portion, said sealed chamber extending radially from said root along the leading edge of said airfoil-shaped portion; a plurality of hollow coolant tubes extending through said sealed chamber and providing coolant passages from the exterior of said blade to said collecting chamber; a liquid metal filling said sealed chamber; and outlet means for exhausting coolant from said collecting chamber.
 6. The invention as defined in claim 5 wherein said liquid is a metal.
 7. The invention as defined in claim 6 wherein said metal is selected from a group consisting of sodium and sodium-potassium alloys.
 8. The invention as defined in claim 5 wherein said outlet means includes a transpiration panel. 